Folic Acid and One-Carbon metabolism--The structure, function, and catalytic properties of the cytoplasmic and mitochondrial forms of the trifunctional conjugated enzyme C1-THF synthase from yeast, and of the corresponding monofunctional bacterial enzymes, 10-formyl- tetrahydrofolate synthetase, 5,10-methylene-tetrahydrofolate dehydrogenase, and 5,10-methenyl-tetrahydrofolate cyclohydrolase, will be examined. These enzymes are involved in the interconversion of three coenzyme forms of the folic acid, a vitamin required by humans for the synthesis and metabolism of proteins, nucleic acids, and other vitamins. The clostridial formyl-THF synthetase, and the yeast cytoplasmic C1-THF synthase will be crystallized for structural analysis. The yeast cytoplasmic and mitochondrial CI-THF synthases will be altered through the use of recombinant DNA techniques to determine the effect of the changes on the function, activity and structure of the proteins. The form of the enzyme that occurs in plants will be determined, and its molecular and genetic relationship to the bacterial and animal enzymes will be determined. Prokaryotic Species-Specific Protein Synthesis--The determinants in messenger RNA responsible for specificity in protein translation other than the Shine-Dalgarno sequence will be determined. This will be done by determining the effect of random changes of nucleotides of the mRNA "window" region on the expression of a gene in B. subtilis compared to expression of that construction in E. coli The characteristics of protein translation will be examined in Micrococcus luteus which is representative of a small group of Gram-positive organisms classified as the "actinomycete" group and is distinguished from other Gram-positive organisms by a variety of properties.